In order to ensure proper operation of a turbine, it is important to set a predefined separation or a predefined annular gap width between the blade tips of the rotor blades and a casing which surrounds the blade tips and which is for example formed by guide vane supports. Such a setting is carried out on an already-assembled turbine, prior to initial startup, as well as before and after carrying out maintenance work.
In a first step, the actual separation between the blade tips and the guide vane supports is measured while the rotor is rotating. To that end, use is made for example of a measurement method in which a metal pin is inserted through a radial through opening provided in the casing until the installer observes contact between the rotor blade tips and the metal pin. The depth of insertion of the metal pin then makes it possible to determine the actual separation present between the blade tips and the casing. Based on the determined actual separation, a further step involves adjusting the relative position of the components. However, one problem of such a separation measurement lies in the fact that it can cause damage to the turbine. If the metal pin is pushed too far into the through opening of the casing, it can be sheared off by the rotating rotor blades and fall into the machine. The consequence of this is that the already fully-assembled turbine has to once again be largely dismantled in order to remove the lost parts from the turbine, which is associated with very high costs.